Voltage regulator for alternator and method of controlling power generation of alternator

ABSTRACT

In an alternator, failure in a power supply line connected to an output terminal of a rectifier is detected. Upon detection of a failure in this power supply line, power generation is suppressed for a predetermined period that is longer than the time constant of a field winding of the alternator. Preferably, a high voltage pulse is detected to discriminate a first condition where a single high voltage pulse is generated when an electrical load connected to the power supply line is cut off and a second condition where a high voltage pulse is repeatedly and frequently generated when a failure occurs in the power supply line. Only when the second condition is discriminated, power generation suppression control of the alternator is conducted.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on and incorporates herein by referenceJapanese Patent Applications No. 2000-313726 filed Oct. 13, 2000 and No.2000-185446 filed Jun. 19, 2001.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a voltage regulator for avehicle alternator and a method of controlling the power generation ofan alternator for a vehicle.

[0003] It is proposed in U.S. Pat. No. 6,191,562 (JP-A-2000-60191) toprotect a power Zener diode of an alternator by improving a drivecircuit of a power transistor so that magnetic energy is dispersed bymaking conductive the power transistor when electric load cut-offcondition is generated. Thus, when a battery is cut off, supply of fieldcurrent from the battery can be stopped.

[0004] However, it has been found that since high voltage is applied tothe field winding of the alternator to increase a field current in thealternator of the structure to supply directly a field current from theDC output terminal of a full-wave rectifier of the alternator, theoutput voltage of the alternator is set in the positive feedbackcondition. Thereby, magnetic energy increases.

[0005] Moreover, when the battery is placed from the condition of beingnot completely cut off, for example, to a condition where the harness isnot perfectly fixed electrically at the output terminal of alternator,or a connection failure occurs anywhere in a power feeding cable,comparatively small surges of voltage are repeatedly applied to thepower Zener diode irregularly within a short period. In this case, alarge amount of heat accumulates because of the repetitive generation ofheat, even though in comparatively small amounts. Therefore thermaldamage becomes larger in this case than in the case where onecomparatively large surge of voltage, such as that generated when arated load is cut off or disconnected is applied.

[0006]FIG. 22 shows changes in temperature T when a reverse current I isrepeatedly generated in the Zener diode. AC voltage is usually generatedin the armature winding. Therefore this voltage becomes high, when afailure occurs. It thereby exceeds the reverse breakdown voltage Vz ofthe Zener diode, and the diode reverse breakdown allows a reversecurrent to flow. This is a rectangular wave current and the frequencythereof depends on the number of rotations of the rotor.

[0007] In this case, an instantaneous value of energy to be consumed inthe Zener diode is given in the form of Vz·Iz (Iz is a reverse currentflowing into one element). This energy is converted to heat and isclassified into the energy accumulated in the thermal capacitance inproportion to the volume of element and the energy dispersed to theexternal side, with thermal resistance to be transferred through amember forming an element (such as electrode, soldering material andsealing material). Therefore, temperature instantaneously rises incomparison with the initial value T0 with the thermal energy accumulatedin the element. Finally, when normal conditions are recovered and highvoltage disappears, the reverse current is cut off and the temperatureof the element is gradually lowered. In this case, if the high voltagecondition is maintained for a long period of time, the temperature ofthe element continuously rises, resulting in the possibility of thermalbreakdown of the element.

[0008] It is also proposed to increase the thermal capacitance byexpanding the area of the diode element. However, mounting becomesdifficult if such an increase of thermal capacitance is realized,because of the spatial limitation on the small size alternator.Moreover, it is also proposed that effective thermal dispersion can berealized by lessening thermal conductivity to the external circuits.However, it is likely that in a usual power generating operationtemperature rises excessively due to radiation of heat from the externalside.

[0009] Moreover, when normal diodes are used for the full-wave rectifierof the alternator, high voltage is not absorbed and appears on the powersupply line. Accordingly, an electrical system protection device of avehicle may be damaged.

SUMMARY OF THE INVENTION

[0010] The present invention therefore has an object to alleviateelectrical and thermal damage to a rectifier of an alternator and avehicle electrical system due to the high voltage that is repeatedlygenerated by the alternator.

[0011] According to the present invention, failure in a power supplyline connected to an output terminal of a rectifier of an alternator isdetected. Upon detection of a failure in this power supply line, powergeneration is suppressed for a predetermined period that is longer thanthe time constant of a field winding of the alternator.

[0012] When a high voltage pulse that is higher than a predeterminedregulated voltage and exceeds a predetermined voltage that is lower thanthe withstand voltage of a rectifier built into an alternator appears atan output terminal of an alternator, this high voltage pulse is detectedto discriminate a first condition where a single high voltage pulse isgenerated when an electrical load connected to the power supply line iscut off and a second condition where a high voltage pulse is repeatedlyand frequently generated when a failure occurs in a power supply line orin a peripheral area. When the second condition is discriminated, powergeneration suppression control of the alternator is conducted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

[0014]FIG. 1 is an electric wiring diagram showing an alternator for avehicle according to a first embodiment of the present invention;

[0015]FIG. 2 is an electric wiring diagram showing a first modificationof the first embodiment;

[0016]FIG. 3 is an electric wiring diagram showing a second modificationof the first embodiment;

[0017]FIG. 4 is an electric wiring diagram showing a third modificationof the first embodiment;

[0018]FIG. 5 is an electric wiring diagram showing a fourth modificationof the first embodiment;

[0019]FIG. 6 is an electric wiring diagram showing a fifth modificationof the first embodiment;

[0020]FIG. 7 is a characteristic diagram showing temperature rise of aZener diode forming a full-ware rectifier in the first embodiment andits modifications;

[0021]FIG. 8 is an electric wiring diagram showing an alternator for avehicle according to a second embodiment of the present invention;

[0022]FIG. 9 is a circuit diagram showing a high voltage pulse detectingcircuit in the second embodiment;

[0023]FIG. 10 is a timing diagram showing signal waveforms inputted oroutputted to or from each section of a voltage control circuit in thesecond embodiment when a high voltage pulse is generated once;

[0024]FIG. 11 is a timing diagram showing signal waveforms inputted oroutputted to or from each section of the voltage control circuit in thesecond embodiment when the high-voltage pulses are generated frequently;

[0025]FIG. 12 is a circuit diagram showing a pulse counting circuit inthe second embodiment;

[0026]FIG. 13 is a timing diagram showing signal waveforms inputted oroutputted to or from each section of the pulse counting circuit in thesecond embodiment;

[0027]FIG. 14 is a circuit diagram showing a high voltage pulsedetecting circuit included in a voltage regulator of an alternator for avehicle according to a third embodiment of the present invention;

[0028]FIG. 15 is a timing diagram showing signal waveforms inputted oroutputted to or from each section of the high voltage pulse detectingcircuit in the third embodiment;

[0029]FIG. 16 is a timing diagram showing comparison of signal waveformsinputted or outputted to or from each section of the high voltage pulsedetecting circuit of FIG. 9;

[0030]FIG. 17 is a circuit diagram showing a high voltage pulsedetecting circuit included in a voltage regulator of an alternator for avehicle according to a fourth embodiment of the present invention;

[0031]FIG. 18 is a timing diagram showing signal waveforms inputted toeach section of the high voltage pulse detecting circuit in the fourthembodiment;

[0032]FIG. 19 is a timing diagram showing signal waveforms inputted toeach section of the high voltage pulse detecting circuit in the fourthembodiment;

[0033]FIG. 20 is a circuit diagram showing a charging system using analternator for a vehicle according to a fifth embodiment of the presentinvention;

[0034]FIG. 21 is a flow diagram showing processing sequence of a CPU inan external controller; and

[0035]FIG. 22 is a characteristic diagram showing a temperature rise ofa Zener diode in a conventional alternator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] The preferred embodiments of the present invention will beexplained with reference to various embodiments and modifications shownin the accompanying drawings.

[0037] [First Embodiment]

[0038] An alternator 1 for a vehicle comprises a three-phase armaturewinding 3, a full-wave rectifier 4, a field winding 5 and a voltageregulator 6. The full-wave rectifier 4 charges an on-board battery 2through a power supply line 8 by converting AC output of the armaturewinding 3 to a DC output. The field winding 5 is wound about a rotorincluding a plurality of field poles to generate an inter-linkagemagnetic flux to induce voltage and forms a field by applying a fieldcurrent. The voltage regulator 6 adjusts DC output voltage of thealternator 1 for a vehicle to a predetermined voltage Vreg.

[0039] The voltage regulator 6 comprises a power transistor 61 reflux orflywheel diode 62, a main power supply circuit 63, a filter 64, a firstcomparator 65, a second comparator 66, a timer circuit 67, an inverter68, an AND gate 69, a pulse generator 70, and an OR gate 71. The secondcomparator 66 is for detecting a failure, while the timer circuit 67 andAND gate 69 are for controlling or suppressing power generation.

[0040] The power transistor 61 is a switch means connected in series tothe field winding 5 for ON/OFF-control of the field current flowing intothe field winding 5. The flywheel diode 62 is a flywheel circuitconnected in parallel with the field winding to flywheel the fieldcurrent when the power transistor 61 is turned off (opened). The mainpower supply circuit 63 detects the turning-on condition of an on-boardkey switch 7 to form the drive power supply, Vcc of the voltageregulator 6 from the on-board battery 2. The filter 64 absorbs harmonicsnoise superimposed on an output voltage of the full-wave rectifier 4.The first comparator 65 compares the output voltage of the filter 64with the predetermined value Vreg, and provides an inverted output whenthe output voltage of the alternator 1 is smaller than the predeterminedvalue Vreg.

[0041] The second comparator 66 compares the output of the filter 64with the predetermined value Vreg+α, and provides an inverted outputwhen the output voltage of the alternator 1 exceeds the predeterminedvalue Vreg+α. The timer circuit 67 inputs the output signal of thesecond comparator 66 and provides an inverted output only for thepredetermined period from a rising edge of the output signal of thesecond comparator 66. This predetermined period is set longer than thetime constant of the field winding 5. The inverter 68 inverts the outputsignal of the timer circuit 67. The AND gate 69 produces a logicalproduct of the output of the first comparator 65 and the output of theinverter 68. The pulse generator 70 generates a clock pulse of low dutyratio. The OR gate 71 produces a logical sum of the output of the ANDgate 69 and the output of the pulse generator 70. The power transistor61 is turned on and off with the output signal of the OR gate 71.

[0042] Next, operations of the voltage regulator 6 of this embodimentwill be explained.

[0043] When the output voltage of the full-wave rectifier 4 is in therange not exceeding Vreg+a, namely when no failure occurs in the powersupply line 8, the output of the inverter 68 becomes high level andtherefore the power transistor 61 is driven in the ordinary voltagecontrol operation.

[0044] When a certain failure occurs in the power supply line 8, forexample, when a contact failure occurs at the connecting point, a sharphigh voltage surge is generated frequently. In this case, if this highvoltage surge is not absorbed with the filter 64 and is then inputted tothe second comparator 66, the second comparator 66 starts the timercircuit 67. During operation of this timer circuit 67, it is preset tooutput the high level signal. Therefore, since output of the AND gate 69is maintained in the low level during this period and the signal of thepulse generator 70 of low duty ratio becomes valid as a drive signal forthe power transistor 61, the power transistor 61 is driven with theoutput signal of this pulse generator 70 to control the supply of thefield current. This low duty ratio is preferably from several percent totens of percent.

[0045] The field current flowing into the field winding 5 is rapidlyattenuated because magnetic energy thereof is converted to thermalenergy with a resistance of the field winding 5 through the flywheeldiode 62. Since the preset period of the timer circuit 67 is longer thanthe time constant of the field winding 5, an average value of the fieldcurrent becomes small and power generation is controlled to the amountto maintain the driving of the main power supply circuit 63. Thereby,charging of the battery 2 is almost stopped. When the timer circuit 67stops the operation thereof, the inverter 68 outputs the high levelsignal. Here, the output voltage of the alternator 1 is lowered becauseit has controlled power generation. Therefore, the first comparator 65provides an inverted output to turn on the power transistor 61. Thereby,power generation is started again. In this case, output voltage exceedsagain the value Vreg+α. The above cycle is repeated to delay theprogress of damage of the defective area of the power supply line 8.Moreover, since chances of generating a high voltage can be reduced,electromagnetic damage to the electrical systems of a vehicle can alsobe controlled.

[0046] [First Modification]

[0047] The first modification of the first embodiment will be explainedwith reference to FIG. 2.

[0048] In this modification, the power transistor 61 is driven with theoutput signal of the AND gate 69, except for the pulse generator 70 oflow duty ratio and the OR gate 71, from the voltage regulator 6 of thefirst embodiment.

[0049] If a certain failure is detected in the power supply line 8,namely when the timer circuit 67 is in the operative condition, thepower transistor 61 is completely turned off and therefore supply of thefield current is stopped. The field current flowing into the fieldwinding 5 rapidly attenuates because the magnetic energy thereof isconverted to thermal energy with the resistance of the field winding 5through the flywheel diode 62. Since the preset period of timer circuit67 is longer than the time constant of the field winding 5, powergeneration is not started again until the field current disappearscompletely. Thereafter, when the timer circuit 67 stops operation, theinverter 68 outputs a high level signal. Here, the output voltage of thealternator 1 is lowered because it has stopped the power generation.Therefore, the first comparator 65 provides an inverted output to turnon the power transistor 61. Thereby, the power generation is startedagain. In this case, when output voltage exceeds Vreg+a, the cycleexplained above is repeated to delay progress of damage on the defectivearea of the power supply line 8. Moreover, chances for generating highvoltage can be reduced, and damage on the electric systems of vehiclecan be controlled.

[0050] [Second Modification]

[0051]FIG. 3 shows a second modification of the first embodiment.

[0052] In this modification, unlike the first modification, thefull-waver rectifier 4 is formed of Zener diodes having the reversebreakdown characteristic to absorb the high voltage surge.

[0053] The voltage regulator 6 is provided with a filter 72 fordetecting the peak value of output voltage of the armature winding 3,and this peak value is compared with a threshold value V1, that islarger than the regulated voltage Vreg, and is smaller than the reversebreakdown voltage Vz of the Zener diode.

[0054] When a failure occurs in the power supply line 8, a high voltagesurge exceeding the reverse breakdown voltage of the Zener diode isnever outputted from the alternator 1. However, the larger the highvoltage surge absorbed with the Zener diode is, the greater the thermaldamage accumulated in the Zener diode becomes.

[0055] According to this modification, when a voltage exceeding V1 isgenerated in the armature winding 3, the second comparator 66 providesan inverted output to turn off the power transistor 61 after themagnetic energy accumulated in the field winding 5 is completelyattenuated, power generation is started again. Therefore, since the heatgenerated in the Zener diode is sufficiently transferred to the externalside, temperature rise due to the reverse breakdown of the Zener diodeis eliminated. This process is shown in FIG. 7. Temperature rise occursonce due to the reverse current I of Zener diode caused by high voltage.Since power generation is immediately stopped, the reverse current I nolonger continues. Therefore, thermal energy generated in the element isreleased to the external side via the structural members. After thetimer circuit 67 stops operation, the reverse current I flows again butpower generation is immediately stopped. As a result, the elementtemperature T reaches a value lower than the initial temperature TO.This temperature T is of course never lower than the externaltemperature. Owing to such a control, thermal damage of the Zener diodecan be controlled to a small extent.

[0056] [Third Modification]

[0057]FIG. 4 shows a third modification.

[0058] In this modification, unlike the first modification, a transistor75 for driving an alarm lamp 89 in the driver's seat is provided so thatthe alarm lamp driving transistor 75 is controlled with an output signalof a timer circuit 67.

[0059] An ordinary failure alarm detecting circuit 73, lights up thealarm lamp 89, by detecting the well known failure mode. An OR gate 74,obtains the logical sum of the output signal of the timer circuit 67,and the output signal of ordinary failure detecting circuit 73.

[0060] Employing this structure, when occurrence of a failure in thepower supply line 8 is detected, supply of the field current stops andthe transistor 75 for driving the alarm lamp 89 is turned off to lightup the alarm lamp 89, in order to notify occurrence of a failure to adriver. When power generation stops due to the generation of highvoltage, the driver is immediately notified. Therefore, generation of afailure can be detected quickly and adequate measures can be takenbefore a failure extends to wider area.

[0061] If the power generation stop period is extended, battery voltageis gradually lowered and a low voltage alarm, which is one of theordinary alarm mode is operated. Thereby, the driver can also benotified of a failure.

[0062] [Fourth Modification]

[0063]FIG. 5 shows a fourth modification.

[0064] In this modification, unlike the second modification, a binarypulse is generated from the output voltage of the armature winding 3 anda failure in the power supply line 8 is detected with a digital counter76.

[0065] The second comparator 66 compares voltage of the power supplyline 8 with the threshold value V2, which is larger than Vreg andsmaller than the reverse breakdown voltage Vz of the Zener diode togenerate a binary pulse signal. Setting is executed to generate highlevel voltage through the inversion when such a binary pulse isgenerated exceeding the predetermined number. Therefore, while thebinary pulse is generated exceeding the predetermined number of pulses,the timer circuit 67 is started and power generation is stopped only forthe predetermined period. With this control method, an operation effectthat is similar to that in the second modification can be attained anddamage to the power supply line 8, alternator 1 and electrical systemsof the vehicle can be alleviated.

[0066] [Fifth Modification]

[0067]FIG. 6 shows a fifth modification.

[0068] In this modification, when a certain failure is detected in thepower supply line 8, the reference value of the first comparator 65,namely the regulated voltage value is set as the second regulatedvoltage value Vreg2, that is smaller than the ordinary value Vreg. Owingto this setting, if a failure is detected, the amount of power generatedcan easily be reduced. The second regulated voltage value is set, forexample, to the value to maintain the minimum voltage to drive thevoltage regulator 6. Owing to this setting, the minimum power to realizere-generation of power after cease of operation of timer circuit can bereached and the alarm function to notify the alarm signal can also bemaintained.

[0069] For example, the second regulated voltage value is preferably setto about one half of the nominal voltage of the on-board battery. Inthis modification, when the timer circuit is in the operative condition,that is, a failure is detected in the power supply line 8, an outputcurrent of only the field current flows into the full-wave rectifier 4,and therefore temperature rise of the rectifying diode can be kept to avery small value.

[0070] In this modification, operation is set to a sequence wherein theoperation mode immediately shifts to the power generation control modeor generation stop mode upon detection of a failure in the power supplyline 8. It is also possible to introduce a sequence, wherein the failuredetecting circuit shifts to the power generation control mode or stopmode when the period, wherein the peak value of the rectifier output orarmature winding output exceeds the predetermined value, continues forthe constant time or longer.

[0071] [Second Embodiment]

[0072]FIG. 8 shows an alternator 1 for a vehicle according to a secondembodiment.

[0073] The alternator 1 for a vehicle comprises an armature winding 3, afull-wave rectifier 4, a field winding 5 and a voltage regulator 6. Thefull-wave rectifier 4 is formed of power Zener diodes for rectifying theAC voltage of the armature winding 3 to DC voltage to have the reversebreakdown characteristics in order to restrict generation of highvoltage pulse when a load is cut off. The output of the full-waverectifier 4 is connected to each electric load 21 of a battery 2 and avehicle.

[0074] The output of the alternator 1 changes depending on the number ofrotations of engine and power feeding to the field winding 5. The fieldcurrent flowing into the field winding 5 is controlled with the voltageregulator 6.

[0075] When a key switch 7 connected to the battery 2 is turned on,supply of the reference voltage Vcc of the voltage regulator 6, and biasvoltage required for operation of each circuit may be started.

[0076] The voltage regulator 6 is formed with an output voltage controlcircuit 77, and a field current control circuit 86. The output voltagecontrol circuit 77 comprises a high frequency noise filter circuit 64,resistors 79, 80, 81, voltage comparator 65, a high voltage pulsedetecting circuit 83, an AND gate 69, and a transistor drive circuit 85.

[0077] The high frequency noise filter circuit 64 eliminates unwantedhigh frequency noise element to protect the voltage control operationfrom the ripple superimposed on an output voltage of the armaturewinding 3 and from the switching noise. A voltage signal having passedthe high frequency noise filter circuit 64 is then inputted to thevoltage comparator 65, and high voltage pulse detecting circuit 83.

[0078] The voltage comparator 65 compares two terminal voltages, one ofwhich is the output voltage of the high frequency noise filter circuit64 and the other of which is the regulated voltage Vreg divided from thereference voltage Vcc with resistors 79 to 81. When a voltage higherthan the regulated voltage Vreg is applied to the negative terminal, theoutput of the voltage comparator 65 becomes low level. When a voltagelower than the regulated voltage Vreg is applied, on the contrary, theoutput of the voltage comparator 65 becomes high level.

[0079] When the high voltage pulse detecting circuit 83, to which anoutput voltage of the high frequency noise filter circuit 64, and thereference voltage V3 divided from the reference voltage Vcc, with theresistors 79 to 81 are applied, detects the high voltage pulse based ontwo kinds of input voltages, this circuit executes the predeterminedsignal process and thereafter provides an output of the low level signalfor the predetermined period. Moreover, if a high voltage pulse is notdetected, the high voltage pulse detecting circuit 83 provides an outputof high level.

[0080] The AND gate 69, to which respective output signals of thevoltage comparator 65 and high voltage pulse detecting circuit 83 areapplied, provides an output of the high level when these input signalsare in the high level and also provides an output of the low level inother cases. The transistor drive circuit 85 executes the on/off controlof the power transistor 61 within the field current control circuit 86depending on the voltage level of input signal.

[0081] The field current control circuit 86 comprises a power transistor61 and a flywheel diode 62 to control a field current flowing into thefield winding 5. The power transistor 61 turns on when an outputterminal of the transistor drive circuit 85 is connected to the gate ofthe power transistor and the output of the transistor drive circuit 85is in the high level. In this timing, the current flowing into the fieldwinding 5 increases. The flywheel diode 62 is connected in parallel withthe field winding 5 to flywheel the field current when the power feedingto the field winding 5 is controlled to OFF state.

[0082]FIG. 9 shows the high voltage pulse detecting circuit 83. The highvoltage pulse detecting circuit 83 comprises a high voltage pulsedetecting section 160, a discriminating section 170, and an outputcontrol section 180. The high voltage pulse detecting section 160 isstructured with a voltage comparator 66. The discriminating section 170is structured with a timer circuit 171, AND gates 172, 174, a pulsecounting circuit 173 and a pulse duration measuring circuit 175. Theoutput control section 180 is structured with a timer circuit 181 and anoutput control circuit 182. The field current control circuit 86corresponds to the field current control means, while the output voltagecontrol circuit 77 to the output voltage control means, the high voltagepulse detecting section 160 to the high voltage pulse detecting means,the discriminating section 170 to the discriminating means and theoutput control section 180 to the output control means, respectively.The timer circuit 171, AND gate 172 and pulse counting circuit 173correspond to the pulse counting means, while the timer circuit 171 tothe timer means and the pulse duration measuring circuit 175 to thepulse duration measuring means, respectively.

[0083] When a high voltage pulse is not generated, the output of thehigh voltage pulse detecting circuit 83 becomes high level and is theninputted to the AND gate 69. The output voltage of the armature winding3 having passed the high frequency noise filter circuit 64 (voltageappearing at the output terminal of the alternator 1) is applied to thenegative terminal of the voltage comparator 65, in which the regulatedvoltage Vreg is applied to the positive terminal. When this inputvoltage is lower than the regulated voltage Vreg, the output becomeshigh level. When this input voltage is higher than the regulated voltageVreg, the output becomes low level and is then inputted to the AND gate69.

[0084] The high (Hi)/low (Lo) conditions of the output of the voltagecomparator 65 are applied to the transistor drive circuit 85 from theAND gate 69. The power transistor 61 is turned on and off by thetransistor drive circuit 85. Thereby, the output voltage of thealternator 1 is adjusted to the predetermined value Vreg (for example,14.5V).

[0085] Next, operations when a high voltage pulse is generated will beexplained.

[0086]FIG. 10 is a timing diagram illustrating the signal waveformsinputted or outputted to or from each section of the voltage regulator 6of this embodiment in the case where one high voltage pulse isgenerated.

[0087] When a comparatively large electric load is cut off, one highvoltage pulse is generated on the power supply line 8. Since the peakvalue of this high voltage pulse is higher than the regulated voltageVreg, an output of the voltage comparator 65 becomes low level and thepower transistor 61 is quickly turned off. Thereafter, when a voltagepulse that is higher than the breakdown voltage of the full-waverectifier 4 formed of the power Zener diode is applied, the power Zenerdiode reaches the breakdown point to absorb the energy of the highvoltage pulse. In order to detect the high voltage pulse, the referencevoltage V3, that is higher than the regulated voltage Vreg and is lowerthan the breakdown voltage is set.

[0088] When the voltage of the power supply line 8 is higher than thisreference voltage V3, the output of the voltage comparator 66 within thehigh voltage pulse detecting section 160 becomes high level. With arising edge of this output signal, operation of the timer circuit 171within the discriminating section 170 is triggered. While the timercircuit 171 is operating, the AND gate 172 outputs directly the outputsignal of the voltage comparator 66. The pulse counting circuit 173 isstructured to maintain an output of low level for the single pulse inputand provide an output of high level for two or more pulse inputs.

[0089] Therefore, when a high voltage pulse is generated once in thepower supply line 8, the output of the pulse counting circuit 173becomes low level and output of the AND gate 174 also becomes low level.In this timing, the pulse duration measuring circuit 175, timer circuit181 and output control circuit 182 do not operate, and the output of theoutput control circuit 182 is maintained at high level. Thereafter, thepeak value of the high voltage pulse is lowered and the output voltageof the alternator 1 is adjusted to the regulated voltage Vreg.

[0090] Next, operation when a high voltage pulse is generated frequentlywill be explained below. FIG. 11 is a timing diagram illustrating signalwaveforms inputted or outputted to or from each section of the voltageregulator 6 of this embodiment when a high voltage pulse is generatedfrequently.

[0091] If a connection failure occurs on the power supply line 8, a highvoltage pulse is generated frequently on the power supply line 8. Whilethe voltage applied to the high voltage pulse detecting circuit 83 ishigher than the reference voltage V3, the output of the voltagecomparator 66 is in the high level. With a rising edge of this outputsignal, operation of the timer circuit 171 is triggered. The timercircuit 171 operates whenever the output of the voltage comparator 66rises and while a high voltage pulse is generated frequently, the outputvoltage becomes high level. Therefore, the AND gate 172 passes theoutput signal of the voltage comparator 66 to the pulse counting circuit173, while the high voltage pulse is generated frequently and the outputof the timer circuit 171 is at the high level.

[0092] When the high voltage pulse is repeatedly applied, the pulsecounting circuit 173 provides an output of high level at the secondrising edge of output of the AND gate 172. This high level condition ofoutput is maintained until a reset pulse (k) is inputted from the timercircuit 181 to the pulse counting circuit 173 and the pulse durationmeasuring circuit 175.

[0093] When the output of the pulse counting circuit 173 becomes highlevel, the AND gate 174 passes the output of the voltage comparator 66to the pulse duration measuring circuit 175 of the next stage. The pulseduration measuring circuit 175 measures the input pulse duration of theoutput signal from the AND gate 174, and also integrates the result ofmeasurement. The durations of the high voltage pulse generatedfrequently are accumulated and when the value exceeds the predeterminedaccumulation period, the output of the pulse duration measuring circuit175 becomes high level.

[0094] When this high level signal is inputted, the timer circuit 181 inthe output control section 180 operates. Thereby the signal inputted tothe output control circuit 182 becomes high level for the predeterminedperiod (for example, 1 sec). While the timer circuit 181 is in theoperative condition, the output control circuit 182 inputs the low levelsignal to the AND gate 69. Thereby, the control operation is executed sothat the power transistor 61 is turned off to stop the power generation.

[0095] In this embodiment, power generation is stopped when output fromthe output control circuit 182 is in the low level. However, it is alsopossible to realize duty-control for the on/off conditions of the powertransistor 61 by presetting output of the output control circuit 182 toalternately repeat the low level and high level conditions in thepredetermined duty ratio.

[0096] Moreover, control of power generation is also allowed throughsetting the power transistor 61 to on/off conditions to set a phasevoltage of a certain phase of the armature winding 3 lower than the openvoltage of the battery 2.

[0097] When the timer 181 terminates the operation, the reset pulse issent to the pulse duration measuring circuit 175 and pulse countingcircuit 173. Thereby the data of the accumulated period and the pulsecounting value are reset.

[0098]FIG. 12 shows the pulse counting circuit 173. As shown in FIG. 12,the pulse counting circuit 173 is structured with a JK flip-flopcircuits 190, 191, a RS flip-flop circuit 192, and inverters 193, 194,195.

[0099]FIG. 13 is a timing diagram illustrating the signal waveformsinputted or outputted to or from each section of the pulse countingcircuit 173.

[0100] Under the condition that the high level signal is inputted to thereset terminals R of the JK flip-flop circuits 190, 191 and RS flip-flopcircuit 192. These flip-flop circuits are reset, and the output Q0 ofthe JK flip-flop circuit 190 and the output Q1 of the JK flip-flopcircuit 191 become low level. Thereby, the output of the inverter 193becomes high level and this high level signal is applied to the inputterminal J of the JK flip-flop circuit 190 of the first stage, while thelow level signal is applied to the input terminal K, respectively.Thereafter, when the reset condition is cancelled, the output Q0 of theJK flip-flop circuit 190 becomes high level in synchronization with therising edge of the pulse signal to be inputted to the clock terminal CK.

[0101] In this case, the output Q1 of the JK flip-flop circuit 191 ofthe second stage is in the low level. Moreover, the output of theinverter 193 changes to the low level, because the output Q0 of the JKflip-flop circuit 191 has become high level. Accordingly, the low levelsignal is inputted to the input terminal J of the JK flip-flop circuit190 of the first stage, and the high level signal to the input terminalK, respectively.

[0102] The output Q1 of the JK flip-flop circuit 191 of the second stagebecomes high level in synchronization with the rising edge of the nextpulse signal, and thereby the output Q0 of the JK flip-flop circuit 190of the first stage becomes low level.

[0103] When the output Q1 of the high level of the JK flip-flop circuit191 is inputted to the input terminal S of the RS flip-flop circuit 192,the output Q of the RS flip-flop circuit 192 becomes high level. Thishigh level condition is maintained until the reset pulse is inputted tothe reset terminal R.

[0104] As explained above, the first input pulse signal of the pulsecounting circuit 173 is made invalid and the second and subsequent pulsesignals are made valid to change the output to the high level.

[0105] The voltage regulator 6 of this embodiment detects conditions ofa high voltage pulse appearing at the output terminal of the alternator1 connected to the power supply line 8, and discriminates the conditionof a single high voltage pulse generated particularly when a failure isnot a connection failure of the power supply line 8 and an electric loadof comparatively large capacitance is no longer used and the conditionof a high voltage pulse that is irregularly and repeatedly generated inthe short period when a connection failure occurs because the powersupply line 8 is not completely disconnected. Therefore, even if acomparatively large electric load is cut off, the power generationcontrol of the alternator 1 is not erroneously responded and an unwanteddrop of the output voltage can be prevented.

[0106] Moreover, when a connection failure occurs in the power supplyline 8, the output of the alternator 1 is controlled, and generation ofhigh voltage pulse applied to the power Zener diode forming thefull-wave rectifier 4 is controlled. The temperature rise of the powerZener diode can also be controlled effectively and thereby thermalbreakdown can be prevented.

[0107] The reverse withstand voltage of the power Zener diode can bethermally designed to have sufficient strength even for the condition toinstantaneously generate a no-load saturation voltage of the alternator1, by cutting off the rated load in the maximum allowable number ofrotations of the alternator 1, namely by electrically cutting off thebattery 2 and electric load 21, during power generation.

[0108] Even in the condition where the output terminal is completelydisconnected, for example, the power supply line 8 and a fusible link 23inserted in series to the power supply line 8 are disconnected (thiscondition is called the “perfect B disconnection”), the power transistor61 for controlling a field current is quickly turned off. Thereby, anenergizing circuit such as the field winding 5 or the like can beprotected. Moreover, the alternator 1 can be protected from breakdown sothat a high voltage pulse generated in the generator output can beabsorbed by the power Zener diode.

[0109] In the condition that an electric load 22 connected directly tothe power supply line 8 without via the fusible link 23 exists, perfectB disconnection occurs. Therefore, even if a comparatively high voltagepulse is generated once, the output control of the alternator 1 is notexecuted. Accordingly, the power can be supplied to the electric load 22connected directly to the power supply line 8 without any drop of theoutput voltage.

[0110] Further, an adequate measure can be taken even when the full-waverectifier 4 is usually formed using the power Zener diode of a lowerwithstand voltage by discriminating the high voltage pulse generatedwith cutting off condition of the load from the high voltage pulsegenerated when a failure occurs. Thereby, an unwanted drop of the outputvoltage for ordinary cut-off of load when the high voltage detectionlevel is lowered can be prevented to cover reduction of the withstandvoltage of the power Zener diode. Such reduction of the withstandvoltage realizes a reduction in the cost of the charging system of thevehicle because the noise appearing on the power supply line 8 can beabsorbed, radiated noise can be reduced and the withstand voltage of thealternator 1 can also be lowered.

[0111] High voltage pulses generated in an irregular manner with theshort period can be detected accurately and temperature rise of powerZener diode can effectively be controlled quickly to prevent thermalbreakdown by comparing, when a connection failure in which the powersupply line 8 is perfectly disconnected, the accumulated period of thehigh voltage pulses generated frequently with the allowable applicationperiod of the power Zener diode.

[0112] In addition, in view of eliminating influence on the voltagecontrol operation of ripples and switching noises, the voltage signalhaving passed the high frequency noise filter circuit 64 is inputted tothe high voltage pulse detecting circuit 83 as another control systemdifferent from the regulated voltage control system. Thereby, since theallowable period of the high voltage pulse is discriminated depending onthe accumulated period of the high voltage pulse, any delay is generatedin the process of the regulated voltage control system. Therefore, whenthe high voltage pulse is generated, the power transistor 61 can beturned off quickly and any adverse effect is not caused in the regulatedvoltage control operation.

[0113] Moreover, if the high voltage pulses are generated repeatedly andthe accumulated period thereof exceeds the allowable application periodof the power Zener diode, the output of the alternator 1 is controlledand thereby generation of a high voltage pulse can also be controlled.Upon completion of the output control of the alternator 1, a reset pulseis generated and the data such as accumulated period of the high voltagepulse and the count number of the pulse counting circuit 173 are reset.Accordingly, if the high voltage pulses are generated repeatedly,detection of the high voltage pulse and control of the power generatingoperation are repeatedly conducted and progress of damage at theconnection failure region of the power supply line 8 can be delayed.Furthermore, since changes for generation of high voltage pulse can bereduced, electric damage on the electric loads 21, 22 can also becontrolled.

[0114] [Third Embodiment]

[0115]FIG. 14 shows a high voltage pulse detecting circuit 83 includedin the voltage regulator 6 of the alternator 1 according to a thirdembodiment.

[0116] The high voltage pulse detecting circuit 83 comprises ahigh-voltage pulse detecting section 160, a discriminating section 170and an output control section 180. This high voltage pulse detectingcircuit 83 is different from the high voltage pulse detecting circuit 83of the second embodiment shown in FIG. 9.

[0117] The discriminating section 170 is provided with a timer 171, ANDgates 172, 174, a pulse counting circuit 173 and a pulse durationmeasuring circuit 175. It further comprises a timer circuit 183 and anOR gate 184. The additional timer circuit 183 receives the input of theoutput signal of the pulse counting circuit 173, while the OR gate 184receives input of each output signal of two timer circuits 181, 183. Theoutput signal of the OR gate 183 is inputted as a reset pulse to thepulse duration measuring circuit 175 and pulse counting circuit 173. Thepulse counting circuit 173 and pulse duration measuring circuit 175correspond to the memory means, while the timer circuit 183, and the ORgate 184 correspond to the reset signal generating means, respectively.

[0118]FIG. 15 shows signal waveforms inputted or outputted to or fromeach section of the high voltage pulse detecting circuit 83 of thisembodiment. FIG. 16 is a diagram for comparing the signal waveforms tobe inputted or outputted to or from each section of the high voltagepulse detecting circuit 83 shown in FIG. 9.

[0119] When connection of an inductive load (for example, a motor torotate an electric fan, or the like) is cut off with a relay or a switchor the like, chattering occurs depending on the response characteristicof the relay or the like. Even when the cut-off operation is performedonce, it is probable that the high voltage pulses are generated severaltimes.

[0120] In the high voltage pulse detecting circuit 83 shown in FIG. 9,if a high voltage pulse higher than the reference voltage V3 isgenerated several times as shown in FIG. 16, the voltage comparator 66outputs the high level signal several times corresponding to such highvoltage pulses. In synchronization with the rising edge of this signal,the timer circuit 171 starts the operation. The AND gate 172 passes theoutput signal of the voltage comparator 66, while the timer circuit 171is in the operative condition. The pulse counting circuit 173 outputsthe high level signal when the pulses are inputted two times or more andthe AND gate 174 outputs the high level signal only for the pulseduration. The pulse duration measuring circuit 175 measures the pulseduration and holds the pulse. Thereafter, since the pulse countingcircuit 173 maintains the high level output, the pulse duration isaccumulated in the pulse duration measuring circuit 175 for eachgeneration, whenever the high voltage pulse is generated due to thecut-off condition of load. When the accumulated duration exceeds thepredetermined accumulated period, the pulse duration measuring circuit175 outputs the high level signal. With this high level signal, thetimer circuit 181 operates, followed by operation of the output controlcircuit 182, to control the power generation output. Accordingly, theoutput voltage of the alternator 1 is lowered. Upon completion ofoperation of the timer circuit 181, the reset pulse is inputted to thepulse duration measuring circuit 175 and pulse counting circuit 173 toreset the data of accumulated period and pulse count number.

[0121] Next, operation to avoid such unnecessary power generationcontrol will be explained with reference to FIG. 15.

[0122] In the high voltage pulse detecting circuit 83 shown in FIG. 14,the timer circuit 183 starts operation when an output of the pulsecounting circuit 173 rises to the high level. This timer circuit 183generates the reset pulse after the predetermined time has passed andthe accumulated period data and pulse count number are reset earlierthan output of the reset pulse from the timer circuit 181. Thereafter, asingle high voltage pulse generated in a certain case because thecut-off condition of load is not accumulated and the output controlcircuit 182 does not operate.

[0123] Even in the case where there is no particular contact failure ofthe power supply line 8, if a high voltage pulse is generated due to thechattering phenomenon when the load is cut off depending on the responsecharacteristic of a relay or the like to control the on/off conditionsof the electric load 21, the output condition and accumulated perioddata of the pulse counting circuit 173 are reset after the predeterminedtime has passed. Thereby, malfunction of power generation control can beprevented.

[0124] The high voltage pulse generated in this case is absorbed by thepower Zener diode forming the full-wave rectifier 4. As explained above,the reverse withstand voltage of power Zener diode is thermally designedparticularly to be resistive to the condition for instantaneouslygenerating a non-load saturation voltage of the alternator 1 withcut-off of the rated load under the maximum allowable number ofrotations of the alternator 1 and therefore such high voltage pulse canbe absorbed with sufficient allowance.

[0125] In addition, since the timer circuit 183 for resetting the dataof the accumulated period can set the time independently, the connectionfailure of the power supply line 8 and chattering phenomenon when theload is cut off can be discriminated easily.

[0126] [Fourth Embodiment]

[0127]FIG. 17 shows a high voltage pulse detecting circuit 83 of thealternator 1 according to a fourth embodiment. This circuit 83 isstructured with a high voltage pulse detecting section 160,discriminating section 170 and output control section 180.

[0128] The discriminating section 170 is similar to that of the thirdembodiment, but it further comprises an OR gate 184, an inverter 185 andan AND gate 186. The discriminating section 170 generates a reset pulsesignal with the timer circuit 171 to input this signal to the one inputterminal of the AND gate 186 and also inputs the signal inverted withthe inverter 185 from the output signal of the pulse duration measuringcircuit 175 to the other input terminal of the AND gate 186. The outputsignal of the AND gate 186 is inputted to the OR gate 184.

[0129]FIG. 18 shows signal waveforms to be inputted to each section ofthe high voltage pulse detecting circuit 83 shown in FIG. 17, whereinthe high voltage pulses are generated several times.

[0130] When a high voltage pulse higher than the reference voltage V3 isgenerated several times, the output of the voltage comparator 66 becomeshigh level corresponding thereto. With the rising edge of this outputsignal, the timer circuit 171 is triggered to operate. The AND gate 172passes, during operation of the timer circuit 171, the output signal ofthe voltage comparator 66 to the pulse counting circuit 173 of the nextstage. Here, the pulse counting circuit 173 outputs the signal of highlevel for the input of the second and subsequent pulses. Therefore, theoutput of the AND gate 174 becomes high level only for the pulseduration. The pulse duration is measured and accumulated with the pulseduration measuring circuit 175. When generation of high voltage pulsestops, operation of the timer circuit 171 also stops and the reset pulseof the timer circuit 171 is generated (FIG. 18(k)).

[0131] The output of the pulse duration measuring circuit 175 maintainsthe low level because the accumulated period of pulse does not reach thepredetermined value (for example, 50 ms). The signal of the high levelthat is generated by inverting such a signal with the inverter 185 isthen inputted to the AND gate 186. In this case, as the output of theAND gate 186, the reset pulse of the timer circuit 171 is outputteddirectly. Since the timer circuit 181 is not operative, the reset pulseoutputted from the timer circuit 181 maintains the low level. Therefore,the OR gate 184 passes directly output of the AND gate 186 to thecircuit of the next stage. Thereby, the reset pulse outputted from thetimer circuit 171 is sent to the pulse duration measuring circuit 175and the pulse counting circuit 173 to reset the accumulated period dataand pulse count number.

[0132]FIG. 19 shows signal waveforms inputted to each section of thehigh voltage pulse detecting circuit 83 shown in FIG. 17. In this case,the high voltage pulses are generated continuously.

[0133] When high voltage pulses are applied, the pulse durations aremeasured and accumulated with the pulse duration measuring circuit 175(FIG. 19(g)). When the high voltage pulses are applied continuously,since the timer circuit 171 does not operate during this period, thereset pulse is not generated with the timer circuit 171. Thereafter,when the pulse duration exceeds the predetermined accumulated period(for example, 50 msec), the output of the pulse duration measuringcircuit 175 becomes high level and thereby the timer circuit 181operates. The output control circuit 182 controls power generation whilethe timer circuit 181 operates (for example, 1 sec).

[0134] Upon completion of the timer circuit 181, the timer reset pulse181 outputs the reset pulse (FIG. 19(n)). When power generation iscontrolled corresponding to operation of the timer circuit 181 andthereby the high-voltage pulse is no longer applied, the timer circuit171 stops operation and the reset pulse is outputted from the timercircuit 171 (FIG. 19(k)). As explained above, the reset pulse isoutputted from the timer circuit 171, but since a signal obtained byinverting the output signal of the pulse duration measuring circuit 175with the inverter 185 is inputted to the AND gate 186, the output of theAND gate 186 is maintained at the low level.

[0135] Therefore, the OR gate 184 passes the reset pulse outputted fromthe timer circuit 181. The reset pulse outputted from the timer circuit181 is then inputted to the pulse duration measuring circuit 175 and thepulse counting circuit 173 to reset the accumulated period data andpulse counter number.

[0136] As explained above, when the accumulated period is 50 msec orless, the timer circuit 171 generates the reset pulse. When theaccumulated period is 50 msec or more, the timer circuit 181 generatesthe reset pulse. Thereby, the number of timer circuits may be reduced torealize reduction in size of the circuit.

[0137] When the output signal of the output control circuit 182 is lowlevel, power generation is stopped. It is also possible to realize theduty-control of the on/off conditions of the power transistor 61 byrepeating the Low and high levels.

[0138] Moreover, it is also possible to use a gradual oscillationcircuit for gradually increasing a duty ratio as the timer circuit 181and output control circuit 182. The timer circuit 181 may be eliminatedunder the condition that a duty ratio preset with the gradualoscillation circuit is lowered to the predetermined value when theoutput of the pulse duration measuring circuit 175 rises and thepredetermined duty ratio can be increased gradually. Generation of ahigh voltage pulse can be controlled effectively by gradually increasingthe duty ratio. Since increase of power generation torque of thealternator can be controlled, a torque shock after re-start of powergeneration can be controlled. In addition, a counter, a capacitor, aresistor, a constant voltage circuit or the like forming the timercircuit 181 may be eliminated by deleting the timer circuit 181 andthereby an IC forming the voltage regulator can be reduced in size.

[0139] [Fifth Embodiment]

[0140] Next, an alternator 1 for a vehicle according to a fifthembodiment will be explained.

[0141]FIG. 20 shows a charging system using the alternator 1 for of thisembodiment. Unlike each embodiment explained above, this embodiment usessoftware to process a high voltage pulse detecting signal.

[0142] The alternator 1 is provided with an armature winding 3, afull-wave rectifier 4, a field winding 5 and a voltage regulator 6. Thisvoltage regulator 6 is provided with a field current control circuit 86,an output voltage control circuit 77 and an FR signal output circuit 13.

[0143] The field current control circuit 86 includes a power transistor61 and a flywheel diode 62 to control the field current flowing throughthe field winding 5. The power transistor 61 is connected at the base tothe output terminal of the output voltage control circuit 77. It turnson when the signal inputted from this output terminal is in the highlevel. In this timing, the current flowing into the field winding 5increases. The flywheel diode 62 is connected in parallel with the fieldwinding 5 and flywheels the field current when power feeding to thefield winding 5 is controlled to off condition.

[0144] The output voltage control circuit 77 sets the first regulatedvoltage (for example, 14.5V) when the signal inputted to the terminal Cis high level and the second regulated voltage (for example, 12.8V) whenthe signal is low level to execute the on/off control of the powertransistor 61.

[0145] The FR signal output circuit 13 outputs from the terminal FR asignal depending on the voltage waveform appearing at the connectingpoint F of the power transistor 61 and the flywheel diode 62.

[0146] The terminals C and FR of the voltage regulator 6 are connectedto an external controller 9. This external controller 9 comprises aninput circuit 90, an output circuit 91, CPU 92 and a memory 93. Thepredetermined process when a high voltage pulse is impressed to thealternator 1 is carried out by executing the predetermined programstored in the memory 93 with the CPU 92.

[0147] The signal outputted from the terminal FR of the voltageregulator 6 is inputted to the input circuit 90, and the predeterminedprocess is executed with the CPU 92. Thereafter, a signal as the resultof this process is then inputted to the terminal C of the voltageregulator 6 from the output circuit 91.

[0148] Here, when a high voltage pulse is applied to the output terminalof the alternator 1 due to a load cut-off condition or a connectionfailure on the power supply line 8, the power transistor 61 is turnedoff and a high voltage pulse is applied to the point F via the fieldwinding 5. Therefore, the high-voltage pulse is outputted to theterminal FR through the output terminal, field winding 5, FR outputcircuit 13 of the alternator 1.

[0149] Next, the high voltage pulse processing procedures within theexternal controller 9 will be explained. FIG. 21 is a flow diagramindicating the processing sequence of the CPU 92.

[0150] First, the CPU 92 detects the output terminal voltage of thealternator 1 based on the signal outputted from the terminal FR (step201) to determine generation or not of a high voltage pulse (step 202).When the high voltage pulse is not generated, a negative determinationis made. Thereafter, the CPU 92 outputs the high level signal to theterminal C to execute the normal power generation control (step 214), sothat the regulated voltage is set to 14.5V. If the high voltage pulse isnot generated, the processes of steps 201, 202, 214 are repeated.

[0151] When the high voltage pulse is applied to the output terminal ofthe alternator 1 due to load cut-off condition or connection failure ofpower supply line 8, positive determination is made (step 202). Next,the CPU 92 initially sets the operating time t of a first timer to 0(step 203), and thereafter compares the timer measuring time t with thepredetermined time t1 (step 204). When t<t1, the CPU 92 counts up thenumber of pulses n (step 205). Here, when the number of pulses n issmaller than 2 (step 206), the processes after step 204 are repeated.

[0152] When the timer measuring time t reaches the predetermined timet1, the process of step 204 shifts to that of step 214 to execute thenormal power generation control.

[0153] When the operating time t of the timer is less than thepredetermined value t1 and the number of pulses n is two or more (step206), the CPU 92 measures the pulse duration (step 207) to calculate theaccumulated period A (step 208). Next, the CPU 92 compares theaccumulated period A with the predetermined time Ar (step 209). When theaccumulated period A is smaller than the predetermined time Ar, theprocesses after step 207 are repeated.

[0154] Meanwhile, when the accumulated period A becomes larger than thepredetermined time Ar, the CPU 92 issues the predetermined failure alarm(step 211) and transmits a signal of low level to the terminal C toconduct power generation control (step 210). This control is continuedfor the predetermined period t2 (for example, 1 sec) (step 212). Inaddition, when the predetermined period t2 has passed, the CPU 92 resetsthe pulse count number n, and the accumulated period A (step 213), andshifts to the normal power generation control (step 214).

[0155] The high voltage pulse appearing at the output terminal of thealternator 1 is detected as explained above. Particularly when a failuresuch as connection failure of the power supply line 8 is not generated,it is possible to discriminate the condition of single high voltagepulse generated when comparatively large capacitance electric load isdisconnected with the condition of the high voltage pulses repeatedlygenerated irregularly within the short period when a contact failure iscontinuously generated because the power supply line 8 is notdisconnected completely. Accordingly, when connection of thecomparatively large capacity electric load is cut off, the outputsuppression control of the alternator 1 is not required as a response tosuch failure and thereby an unwanted drop of output voltage can beavoided.

[0156] Moreover, when a connection failure of the power supply line 8 isgenerated, the output of the alternator 1 is controlled to suppressgeneration of a high voltage pulse applied to the power Zener diodeforming the full-wave rectifier 4. Thereby, temperature rise of powerZener diode can be suppressed effectively to prevent thermal breakdown.

[0157] In addition, since it is also possible to notify the driver ofthe generation of a failure on the power supply line 8 with the issuanceof an alarm for the failure by discriminating the conditions of the highvoltage pulses generated repeatedly, such a failure can be found quicklyand irregular processes can also be prevented.

[0158] Moreover, in the structure of this embodiment, the existingsystem configuration can be used directly for the hardware of thevoltage regulator 6 of the alternator 1. It can also be covered with anupdate of the software (program) to be executed in the CPU 92 of theexternal controller 9. Thereby, rise of costs due to system alterationcan be minimized.

[0159] In this embodiment, the alternator 1 is isolated from theexternal controller 9, but these elements can also be integrated.

[0160] In this embodiment, the external controller 9 switches outputvoltage of the alternator 1 by sending a signal to the terminal C fromthe output circuit 91, but it is also possible to change the applicationcondition of a load by sending an instruction for the switching of anelectric load from the output circuit 91.

[0161] The present invention should not be limited to the disclosedembodiments and modifications, but may be implemented in various wayswithout departing from the spirit of the invention.

What is claimed is:
 1. A voltage regulator for controlling an outputvoltage of an alternator having a field winding, an output terminalconnected to a battery through a power supply line, the voltageregulator comprising: a field current control means connected to thefield winding for controlling the field current of the field winding;and an output voltage control means for controlling the field currentcontrol means by detecting at least one of an output voltage of thealternator and a terminal voltage of the battery, wherein the outputvoltage control means includes: a high voltage pulse detecting means fordetecting a high voltage pulse that is larger than a predeterminedregulated voltage and exceeds a predetermined voltage that is smallerthan a withstand voltage of a rectifier provided in the alternator, whenit appears at the output terminal of the alternator; a discriminatingmeans for discriminating a first condition where a single high voltagepulse is generated when an electrical load connected to the power supplyline is cut off and a second condition where the high voltage pulse isfrequently and repeatedly generated when a failure occurs in the powersupply line; and an output control means for suppressing powergeneration of the alternator when the second condition is discriminatedby the discriminating means.
 2. The voltage regulator as in claim 1,wherein the failure that generates the high voltage pulses in the secondcondition is a connection failure occurred on the power supply line, andwherein the suppressing means suppresses a supply of field current tothe field winding only when the second condition is discriminated inorder to suppress power generation of the alternator.
 3. The voltageregulator as in claim 2, wherein the discriminating means includes: apulse counting means for counting the number of high voltage pulsesignals; and a pulse duration measuring means for measuring a pulseduration of the high voltage pulses.
 4. The voltage regulator as inclaim 3, wherein the pulse counting means includes a timer means tooperate for a predetermined time from the input of the high voltagepulse signal in order to discriminate the first and second conditionsbased on the number of the pulse signals to be inputted during operationof the timer means.
 5. The voltage regulator as in claim 4, wherein thepulse duration measuring means accumulates the duration of the highvoltage pulse signal when the second condition is discriminated with thepulse counting means to determine the failure only when the accumulatedduration exceeds a predetermined value.
 6. The voltage regulator as inclaim 2, wherein the discriminating means includes a storage means forstoring the condition of the high voltage pulse as data and a resetsignal generating means for resetting the data stored in the storagemeans after a predetermined time has passed.
 7. A method for controllingpower generation of an alternator for a vehicle comprising steps of:detecting a high voltage pulse that is larger than a predeterminedregulated voltage and exceeds a predetermined voltage smaller than awithstand voltage of a rectifier built in the alternator, when the pulseappears at an output terminal of the alternator; discriminating a firstcondition where a single high voltage pulse is generated when anelectric load connected to a power supply line is cut off and a secondcondition where the high voltage pulse is frequently and repeatedlygenerated when a failure occurs in the power supply line; andsuppressing power generation of the alternator when the second conditionis discriminated.
 8. A voltage regulator for an alternator having afield winding, an armature winding, a full-wave rectifier connected withthe armature winding, an output terminal of the full-wave rectifierconnected to a battery through a power supply line, the voltageregulator comprising: a field current control device connected in serieswith the field winding, which supplies field current to the fieldwinding in response to a control signal; and an output voltageregulating circuit connected with the field current control device,which generates the control signal to regulate output voltage of thealternator; a high voltage pulse detecting circuit connected with theoutput terminal, which detects a high voltage pulse of which voltage iswithin a range between a regulated voltage regulated by the outputvoltage regulating circuit and a voltage that is smaller than awithstand voltage of a rectifier element provided in the full-waverectifier; a discriminating circuit connected with the high voltagepulse detecting circuit, which discriminates a serial high voltagepulses from a non-serial high voltage pulse indicative of disconnectionof an electrical load from the power supply line; and a suppressingcircuit connected with the discriminating circuit, which modulates thecontrol signal to suppress power generation of the alternator inresponse to a discrimination of the serial high voltage pulses.
 9. Thevoltage regulator as in claim 8, wherein the suppressing circuitincludes a gate circuit which blocks the control signal from the voltageregulator in response to a signal from the discriminating circuit. 10.The voltage regulator as in claim 9, wherein the discriminating circuitincludes: a timer circuit which generates the signal to be applied tothe gate circuit for a predetermined time; and a detecting circuit whichdetects the serial high voltage pulse including at least two of highvoltage pulses, and initiates the timer circuit in response to adetection of the serial high voltage pulses.
 11. The voltage regulatoras in claim 10, wherein the detecting circuit includes: a pulse durationmeasuring circuit which accumulates duration of the high voltage pulsesand initiates the timer circuit when the accumulated duration reaches toa predetermined time.
 12. The voltage regulator as in claim 11, whereinthe detecting circuit further comprises: a pulse counting circuitconnected with the high voltage pulse detecting circuit, which countsnumber of high voltage pulse detecting circuit, which counts number ofhigh voltage pulses and enables the pulse duration measuring circuit toaccumulate duration when the count of high voltage pulses reaches atleast two.